Single mag amp control system for regulating bipolar voltage output of a power converter

ABSTRACT

A power converter embodying the principles of the invention, and having a positive and negative output utilizes a single magnetic amplifier controller to control two saturable inductor cores utilized to regulate the positive and negative outputs by modulating the positive and negative pulse output of the power converter transformer. The magnetic amplifier controller monitors and sums the two voltage outputs and derives an offset from average representative output signal. This offset from average representative output signal is compared with a reference signal to derive an error signal. A current responsive to the error signal is generated and utilized to periodically reset the two saturable inductor cores and regulate the positive and negative output voltages.

FIELD OF THE INVENTION

This invention relates to power supplies having multiple outputs and inparticular to power supplies using magnetic amplifiers to regulate theoutput.

BACKGROUND OF THE INVENTION

A multiple output power supply whose output is regulated by usingmagnetic amplifiers conventionally has two saturable inductor cores ineach output and a separate magnetic amplifier controller for eachoutput. While this provides precise regulation, the number of magneticcores required and the need for a separate magnetic amplifier controllerfor each output is expensive and often provides regulation with moreprecision than is needed for a particular application.

SUMMARY OF THE INVENTION

A two output power converter, embodying the principles of the invention,utilize a single magnetic amplifier controller to control two saturableinductor cores utilized to regulate the positive and negative outpus ofa converter by modulating the positive and negative pulse output of thepower converter transformer. The magnetic amplifier controller monitorsand sums the two voltage outputs and derives an offset from averagerepresentative output signal. This offset from average representativeoutput signal is compared with a reference signal to derive an errorsignal. A current responsive to the error signal is generated andutilized to periodically reset the two saturable inductor cores andregulate the positive and negative output voltages.

BRIEF DESCRIPTION OF THE DRAWING

An understanding of the invention may be readily attained by referenceto the drawing in which:

FIG. 1 is a schematic of a power converter embodying the principles ofthe invention; and

FIG. 2 is is a schematic of a magnetic amplifier controller suitable forapplication to the power converter of FIG. 1.

DETAILED DESCRIPTION

A power converter embodying the principles of the invention is shown inFIG. 1, It includes an inverter switching circuit 101 which switches aDC voltage supplied by a DC energy source applied to input terminals 102and 103. This inverter switching circuit 101 is not shown in detailsince inverter switching circuits are well known in the art. It operatesby periodically switching the applied DC voltage to produce an AC pulsesignal which is applied to the primary winding 106 of power transformer105. A secondary winding of the power transformer is center tapped atnode 104 to produce two secondary windings 107 and 108 connected inseries with each other. The center tap (node 104) is connected via lead110 to a return terminal 111 which is common to two output terminals 112and 113 which supply regulated DC voltage outputs of opposite polarity.A positive DC voltage output is supplied at terminal 112 and a negativeDC voltage output is supplied to terminal 113.

A regulated positive DC voltage output at output terminal 112 is derivedfrom secondary winding 107 when its pin 1 is positive with respect tothe node 104. This voltage is coupled to the positive output terminal112 through the magnetic amplifier winding 121 of magnetic amplifiercore 120, rectifying diode 131 and winding 141 of filter inductor coil140.

A regulated positive DC output voltage is also derived from secondarywinding 108 when its pin 2 is positive with respect to the node 104 andis coupled to the output terminal 112 through winding 126 of magneticamplifier core 125, rectifying diode 132 and winding 141 of filter coil140.

Similarly a regulated negative DC voltage output is derived at outputterminal 113 from secondary winding 108 when its pin 2 is positive withrespect to the node 104. This voltage is coupled to the negative outputterminal 113 through the magnetic amplifier winding 126 of magneticamplifier core 125, rectifying diode 132 and winding 142 of filterinductor coil 140.

A regulated negative DC output voltage is also derived from secondarywinding 107 when its pin 1 is negative with respect to the node 104 andis coupled to the output terminal 113 through winding 127 of magneticamplifier core 126, rectifying diode 133 and winding 142 of filter coil140.

Regulation of the DC output voltage at terminals 112 and 113 iscontrolled by a single magnetic amplifier controller 150. The magneticamplifier controller 150 monitors the positive and negative outputvoltages at output terminals 112 and 113 via leads 152 and 153,respectively. It sums the two sensed voltage outputs and derives anoffset voltage representative of an average output voltage Thisrepresentative offset voltage of the average output voltage is comparedwith a reference voltage and an error voltage is generated. A currentresponsive to the error voltage is generated and applied on lead 151wherein it is transmitted via diodes 156 and 157, which are switched bythe voltage polarities, to transmit the reset current and periodicallyreset the two saturable inductor cores 120 and 125. While arepresentative voltage of the average output voltage is derived in thisparticular example with regulated output voltages of opposite polarity aconventional average voltage could be used if the two output voltageswere of the same polarity.

An understanding of the invention may be readily attained by describingthe operation of the circuit. The inverter switching circuit 101 appliesa train of pulses of alternating polarity to the primary winding 106.Assume that a pulse in the secondary winding 17 is positive at pin 1 ofthat winding with respect to the center tap 104. Initially thetransmission of this pulse is to the output 112, via inductor winding121, is blocked by the inductance of the saturable inductor core 120.The time delay of the leading edge of the pulse caused by this block isdetermined by the level at which the core was reset followingtransmission of the previous pulse transmitted. At the end of this timedelay the positive pulse is transmitted and goes via rectifying diodes131 and 132 and the output filter comprising capacitor 161 and inductorwinding 141 to the positive output terminal 112.

A negative output is supplied at output terminal 113 from the negativepin 2 of winding 108 and after the time delay determined by the resetlevel of saturable inductor core 120 is transmitted by winding 122 andcapacitor 134 to the output filter comprising capacitor 162 and inductorwinding 142 and from there to output terminal 113.

A similar process occurs when pin 2 of winding 108 becomes positive.Winding 126 of the saturable inductor core 125 delays the pulse asdetermined by the reset level to which it was set following transmissionof the previous pulse. The rectifying diodes 132 and 133 rectify thepositive and negative pulses respectively. Capacitor 162 and filterwinding 141 filters the positive pulse and capacitor 162 and filterwinding 142 filters the negative pulse. Hence a positive DC outputvoltage appears at output terminal 112 and a complimentary negative DCoutput voltage appears at output terminal 113.

The DC voltage outputs at terminals 112 and 113 are sensed and coupledvia leads 152 and 153 to the magnetic amplifier controller 150. Themagnetic amplifier controller 150 sums the magnitude of both the sensedoutput voltages to obtain offset representation voltage which isrepresentative of the average magnitude of the two output voltages. Thisrepresentative voltage is compared with a fixed reference voltage levelby an error amplifier to obtain an error voltage. This error voltage ofthe error amplifier is transformed to a reset current for the twomagnetic amplifier cores 120 and 125.

This reset current is applied to the magnetic amplifier core 120 throughdiode 137 when the pulse train a pin 1 of winding 107 is negative withrespect to the center tap node 104. Similarly a reset current is appliedto the magnetic amplifier core 125 through diode 138 when the pulsetrain is negative at pin 2 of winding 108 with respect to the center tapnode 104. This reset current periodically resets the magnetic amplifiercores 120 and 125 by the exact amount necessary to maintain the averageoutput voltage magnitude at a desired regulated value when the load atthe outputs 112 and 113 varies or is changed.

Two free wheeling diodes 163 and 166 are included to maintain continuityof current in the filter windings 141 and 142 for both positive andnegative currents during dead time pulses and diode blocking of thepulse train.

An illustrative controller is disclosed in FIG. 2. The two outputvoltages are coupled, via leads 252 and 253, to an offset voltagedivider comprising the resistors 270 and 271 which are selected to bedifferent in value. This voltage divider sums the two opposite polarityoutput voltages and derives a voltage representative of an averagevoltage value at the two output terminals. This representative voltageis applied to an error amplifier 272 which compares it to a referencevoltage 273 and generates an error voltage which it applies to atransconductance amplifier 274. The transconductance amplifier 274converts the error voltage to reset current which appears on its outputlead 252 connected to the cores of the saturable inductors.

We claim:
 1. A power supply with at least a first and second output,comprising:a first saturable inductor in series with the first output, asecond saturable inductor in series with the second output, means forsensing an output voltage at both the first and second outputs, amagnetic amplifier controller adapted to sum the output voltages sensedby the means for sensing and derive a control voltage representative ofan average output voltage and compare it to a reference voltage toobtain a reset current, means for applying the reset current to resetthe first and second saturable inductors.
 2. A power supply as claimedin claim 1 further including a power transformer having a primary andsecondary winding,an inverter switching circuit connected to the primarywinding, the first saturable inductor having a first and second winding,the second saturable inductor having a first and second winding, thesecondary winding being centertapped and the first winding of the firstsaturable inductor connected to a first terminal end of the secondarywinding and the first winding of the second saturable inductor beingconnected to a second terminal end of the secondary winding, the secondwinding of the first saturable inductor being connected to the secondterminal end of the secondary winding and the second winding of thesecond saturable inductor being connected to the first terminal end ofthe secondary winding, and the means for applying the reset currentbeing connected to the first winding of the first and second saturableinductors.
 3. A power supply as claimed in claim 2 and furtherincludingfirst rectifying means for coupling positive voltages from thefirst winding of each of the first and second saturable inductors to thefirst output, and second rectifying means for coupling negative voltagesfrom the second winding of each of the first and second saturableinductors to the second output.
 4. A power supply as claimed in claim 3and further including diode means oriented to periodically enablecurrent flow in the means for applying the reset current.
 5. A powersupply as claimed in claim 4 and further including a filter inductorhaving a first and second winding connected in series with the first andsecond output respectively.
 6. A power supply as claimed in claim 5 andfurther including means for assuring current continuity in the first andsecond windings of the filter inductor.
 7. A power supply as claimed inclaim 6 wherein the magnetic amplifier controller includes a voltagedivider connected to the first and second outputs and having unequalfirst and second impedances in order to generate a voltagerepresentative of an average of the two output voltages.